doctests: use julia lts (#652)

Author: benlorenz

.github/workflows/Documenter.yml

@@ -13,7 +13,7 @@ jobs:
     steps:
       - uses: julia-actions/setup-julia@v2
         with:
-          version: '1'
+          version: 'lts'
           show-versioninfo: true         # print versioninfo in the action log
       - uses: actions/checkout@v4
       - uses: julia-actions/julia-buildpkg@latest